Expression and function of a large non-coding RNA gene XIST in human cancer

Background: X inactive-specific transcript (XIST) RNA is involved in X chromosome silencing in female cells and allows X chromosome equilibration with males. X inactive-specific transcript expression has been found to be dysregulated in a variety of human cancers when compared to normal cells; meanwhile, the inactivated X chromosome has been noted to be conspicuously absent in human cancer specimens, whereas X chromosome duplications are widely noted. The specific pathways whereby changes in X chromosome status and XIST expression occur in cancer remain incompletely described. Nevertheless, a role for XIST in BRCA1-mediated epigenetic activity has been proposed. Methods: Here we review the data regarding XIST expression and X chromosome status in a variety of female, male, and non-sex-related human cancers. Conclusions: It is not yet known whether X chromosome duplication, XIST dysregulation, and over-expression of X-linked genes represent important factors in tumorgenesis or are simply a consequence of overall epigenetic instability in these cancers.